/Engine/Source/Editor/UnrealEd/Public/FbxImporter.h
When we get exported time we call GetanimationInterval from fbx sdk and it return the layer 0 by default This function return the sum of all layer instead of just the layer 0.
void GetAnimationIntervalMultiLayer ( FbxNode * RootNode, FbxAnimStack * AnimStack, FbxTimeSpan & AnimTimeSpan )